Propeller fan and axial flow blower

ABSTRACT

A stagger angle of a rotor blade has a first stagger angle distribution having a local minimum value in a region from an inner circumferential edge to a first boundary position, and has a second stagger angle distribution that increases toward an outer circumferential edge and follows an n-dimensional function using the radius of the rotor blade as a parameter in a region from the first boundary position to the outer circumferential edge, where n is a value ranging from 1 to 2 and exclusive of 1. This can limit the height of the outer circumferential portion, and can achieve a reduced noise level and higher efficiency.

FIELD

The present invention relates to a propeller fan and to an axial flowblower for use in a ventilation fan, an air conditioner, and the like.

BACKGROUND

To achieve a reduced noise level, a rotor blade of a propeller fan of anaxial flow blower has been improved to be swept forward in the rotationdirection and to be inclined toward the upstream side of an airflow. Inrecent years, to achieve a further reduced noise level, it has beenproposed that an outer circumferential part of a rotor blade be benttoward the upstream side of an airflow to reduce interference caused byblade tip vortex.

Patent Literature 1 describes that rotor blades are each inclined towardthe upstream side at a certain first forward tilt angle in an innercircumferential portion of the rotor blade, while the rotor blades areeach inclined toward the upstream side at a second forward tilt anglegreater than the first forward tilt angle in an outer circumferentialportion.

Patent Literature 2 describes that a stagger angle of the blade islinearly increased from the inner circumferential edge to the outercircumferential edge. Patent Literature 2 also describes that thestagger angle in an inner circumferential portion side has adistribution having a local minimum value, and the stagger angle in anouter circumferential portion side has a distribution having a localmaximum value.

Patent Literature 3 describes that an angle of advance in an innercircumferential portion side of a rotor blade has a distribution of aquadratic function, while an angle of advance in an outercircumferential portion side thereof has a linear distribution.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent No. 4680840

Patent Literature 2: Japanese Patent No. 6005256

Patent Literature 3: Re-publication of PCT International Publication No.WO 2015/125306 A1

SUMMARY Technical Problem

Setting of geometry parameters as described in Patent Literatures 1 to 3enables a reduced noise level to be achieved and fan efficiency to beimproved. Nevertheless, there has been a demand to change a geometryparameter based on which further improvement in performance can beachieved.

The present invention has been made in view of the foregoingcircumstances, and it is an object of the present invention to provide apropeller fan and an axial flow blower that can further reduce the noiselevel and further improve the fan efficiency.

Solution to Problem

In order to solve the above-mentioned problems and achieve the object,the present invention provides a propeller fan including a boss portionthat is driven rotationally, and more than one rotor blade radiallyattached to the boss portion to generate an airflow in a rotational axisdirection, wherein a radial cross section of the rotor blade on an innercircumferential portion side of the rotor blade has a shape convexagainst a direction of the airflow, and a radial cross section of therotor blade on an outer circumferential portion side of the rotor bladehas a shape concave along the direction of the airflow, the radial crosssection of the rotor blade is inclined toward an upstream side of theairflow in a leading edge side region with an inclination angleincreasing toward a leading edge, and is inclined toward a downstreamside of the airflow in a trailing edge side region with the inclinationangle increasing toward a trailing edge, and a stagger angle of therotor blade has a first stagger angle distribution having a localminimum value in a region from an inner circumferential edge to a firstboundary position, and has a second stagger angle distribution thatincreases toward an outer circumferential edge and follows ann-dimensional function using a radius of the rotor blade as a parameterin a region from the first boundary position to the outercircumferential edge, where n is a value ranging from 1 to 2 andexclusive of 1.

Advantageous Effects of Invention

The present invention enables a rotor blade to have a shape suitable foran airflow over a region from an inner circumferential edge to an outercircumferential edge, and can thus reduce noise possibly caused by ablade tip vortex and improve fan efficiency.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view illustrating an example of an axial flowblower.

FIG. 2 is a perspective view illustrating an example of a propeller fan.

FIG. 3 is a schematic view illustrating generation of a blade tipvortex.

FIG. 4 is a cross-sectional view of a rotor blade of the presentembodiment, taken along a radial direction of the blade.

FIGS. 5A-5D are diagrams schematically illustrating a cross-sectionalshape of a rotor blade of the present embodiment, a blade tip vortex,and a radial flow at a number of cross-sectional positions.

FIG. 6 is a diagram illustrating different cross-sectional positions.

FIG. 7 is a diagram illustrating a positional relationship between arotor blade and a half bell mouth.

FIG. 8 is a diagram illustrating a positional relationship between arotor blade and a full bell mouth.

FIG. 9 is a diagram illustrating a state of airflow to a rotor bladewhen a half bell mouth is used.

FIG. 10 is a diagram illustrating a state of airflow to a rotor bladewhen a full bell mouth is used.

FIG. 11 is a diagram for describing a definition of a stagger angle.

FIG. 12 is a diagram illustrating an example of a distribution of thestagger angle of a rotor blade of the present embodiment.

FIG. 13 is a diagram illustrating distributions of stagger angles of therotor blades in Comparative Example 1 and Comparative Example 2.

FIG. 14 is a developed sectional view illustrating comparison betweenthe stagger angle in Comparative Example 1 and the stagger angle inComparative Example 2 in a first region.

FIG. 15 is a developed sectional view illustrating comparison betweenthe stagger angle in Comparative Example 1 and the stagger angle inComparative Example 2 in a second region.

FIG. 16 is a schematic view illustrating a rotor blade of ComparativeExample 1.

FIG. 17 is a schematic view illustrating a rotor blade of ComparativeExample 2.

FIG. 18 is a diagram for describing a definition of an angle of advance.

FIG. 19 is a graph illustrating an example of a distribution of an angleof advance of the rotor blade of the present embodiment.

FIG. 20 is a plan view illustrating a blade shape of Comparative Example3 when an increase rate in the angle of advance is lower.

FIG. 21 is a plan view illustrating a blade shape of Comparative Example3 when an increase rate in the angle of advance is higher.

FIG. 22 is a plan view illustrating a rotor blade of the presentembodiment.

FIG. 23 is a diagram for describing a definition of a forward tiltangle.

FIG. 24 is a diagram illustrating a chord center line of a rotor bladeof the present embodiment.

FIG. 25 is a graph illustrating an example of a distribution of aforward tilt angle of a rotor blade of the present embodiment.

FIGS. 26A-26C are diagrams illustrating a fan efficiency characteristic,a specific noise characteristic, and a static pressure characteristic ofa rotor blade of Example 1, Example 2, and Comparative Example 5 in acase of use of a half bell mouth.

FIGS. 27A-27C are diagrams illustrating a fan efficiency characteristic,a specific noise characteristic, and a static pressure characteristic ofa rotor blade of Example 1, Example 2, and Comparative Example 5 in acase of use of a full bell mouth.

FIGS. 28A-28C are diagrams illustrating a fan efficiency characteristic,a specific noise characteristic, and a static pressure characteristic ofa rotor blade of Example 1, Example 3, and Comparative Example 5 in acase of use of a half bell mouth.

FIGS. 29A-29C are diagrams illustrating a fan efficiency characteristic,a specific noise characteristic, and a static pressure characteristic ofa rotor blade of Example 1, Example 3, and Comparative Example 5 in acase of use of a full bell mouth.

FIG. 30 is a graph illustrating relationships between the degree of theforward tilt angle distribution function and the specific noise level inExample 1 and Comparative Example 5 in a case of use of a half bellmouth.

FIG. 31 is a graph illustrating relationships between the degree of theforward tilt angle distribution function and the fan efficiency inExample 1 and Comparative Example 5 in a case of use of a half bellmouth.

FIG. 32 is a graph illustrating relationships between the degree of theforward tilt angle distribution function and the minimum specific noiselevel in Example 1 and Comparative Example 5 in a case of use of a halfbell mouth.

FIG. 33 is a graph illustrating relationships between the degree of theforward tilt angle distribution function and the maximum fan efficiencyin Example 1 and Comparative Example 5 in a case of use of a half bellmouth.

FIG. 34 is a graph illustrating relationships between the degree of theforward tilt angle distribution function and the specific noise level inExample 1 and Comparative Example 5 in a case of use of a full bellmouth.

FIG. 35 is a graph illustrating relationships between the degree of theforward tilt angle distribution function and the fan efficiency inExample 1 and Comparative Example 5 in a case of use of a full bellmouth.

FIG. 36 is a graph illustrating relationships between the degree of theforward tilt angle distribution function and the minimum specific noiselevel in Example 1 and Comparative Example 5 in a case of use of a fullbell mouth.

FIG. 37 is a graph illustrating relationships between the degree of theforward tilt angle distribution function and the maximum fan efficiencyin Example 1 and Comparative Example 5 in a case of use of a full bellmouth.

DESCRIPTION OF EMBODIMENT

A propeller fan and an axial flow blower according to an embodiment ofthe present invention will be described in detail below with referenceto the drawings. Note that this embodiment is not intended tonecessarily limit the scope of this invention.

Embodiment.

FIG. 1 is a perspective view illustrating an example of an axial flowblower 100 according to an embodiment. FIG. 2 is a perspective viewillustrating an example of a propeller fan 10 according to theembodiment. The axial flow blower 100 includes the propeller fan 10, abody 20, a bell mouth 30, a motor (not illustrated), and a motor fixingmember (not illustrated). The propeller fan 10 and the motor aredisposed inside the bell mouth 30. The propeller fan 10 includes a bossportion 2 having a cylindrical shape, and multiple rotor blades 1 havingequal three-dimensional shapes.

The boss portion 2 is rotationally driven by the motor to rotate about arotational axis O in a direction of an arrow W. Each of the rotor blades1 is radially attached to an outer periphery of the boss portion 2. Therotor blade 1 includes: a leading edge 1 a that is a front edge portionin the rotation direction W; a trailing edge 1 b that is a rear edgeportion in the rotation direction W; an inner circumferential edge 1 cthat is an edge portion on the inner circumferential side (nearer to theboss portion 2); and an outer circumferential edge 1 d that is an edgeportion on the outer circumferential side. Rotation of the propeller fan10 causes the rotor blades 1 to generate an airflow in a direction of anarrow A. FIG. 1 illustrates five of the rotor blades 1, and FIG. 2illustrates three of the rotor blades 1. As the number of rotor blades1, any other number can also be adopted.

FIG. 3 illustrates one of the impeller blades 1 of the propeller fan 10.When an airflow in the arrow A direction is generated by rotation of thepropeller fan 10, a pressure difference is caused between the bladepressure surface and the blade negative pressure surface of the rotorblade 1. As illustrated in FIG. 3, this leads to a leakage vortex fromthe blade pressure surface subject to a higher pressure to the bladenegative pressure surface subject to a lower pressure, in an outercircumferential portion of the rotor blade 1. This vortex is referred toas a blade tip vortex 5. As illustrated in FIG. 4, the upstream bladesurface is a negative pressure surface if subject to the lower pressure,and the downstream surface is a pressure surface 1 g subject to a higherpressure with respect to the airflow direction A. Note that in thefollowing description, the rotational axis O is designated Z-axis, andtwo axes perpendicular to the Z-axis are designated X-axis and Y-axis.

FIG. 4 is a cross-sectional view illustrating the shape, along theradial direction, of the rotor blade 1 according to the embodiment. Therotor blade 1 has a radial cross section that is convex against theairflow direction A near the boss portion 2, and is concave in theairflow direction A in an outer circumferential portion. In other words,the rotor blade 1 has a vertex portion m1 having a convex shape on aninner circumferential portion side, and a vertex portion m2 having aconcave shape on an outer circumferential portion side. Thus, a crosssection of the rotor blade 1 has an S-shape that is convex with respectto the airflow in an inner circumferential portion, and is concave withrespect to the airflow in an outer circumferential portion.

The rotor blade 1 also has a radial cross-sectional shape changing overthe region from the leading edge 1 a to the trailing edge 1 b.Specifically, in a leading edge region, the rotor blade 1 is inclinedtoward upstream of the airflow direction A so that an inclination angleθ increases toward the leading edge 1 a. In a trailing edge region, therotor blade 1 is inclined toward downstream of the airflow direction Aso that the inclination angle θ increases toward the trailing edge 1 b.FIGS. 5A to 5D are diagrams schematically illustrating the blade shape,a blade tip vortex, and a radial flow in the radial cross section of therotor blade 1 according to the embodiment. FIG. 5A illustrates thecross-sectional shape taken along a line O-D1 in FIG. 6. FIG. 5Billustrates the cross-sectional shape taken along a line O-D2 in FIG. 6.FIG. 5C illustrates the cross-sectional shape taken along line O-D3 inFIG. 6. FIG. 5D illustrates the cross-sectional shape taken along lineO-D4 in FIG. 6. Note that, in FIG. 6, the line O-D1 is a line resultingfrom extending a line connecting the rotational axis O and a rear end Frof the leading edge 1 a to the outer circumferential edge 1 d; and theline O-D4 is a line connecting the rotational axis O and a front end Rfof the trailing edge 1 b.

As illustrated in the O-D1 cross section and in the O-D2 cross section,a leading edge region of the rotor blade 1, which is an area nearer tothe leading edge 1 a than a blade center C, is inclined toward upstreamof the airflow A, and the inclination angle θ(O-D1) in the O-D1 crosssection is greater than the inclination angle θ(O-D2) in the O-D2 crosssection. In other words, in the leading edge region, the inclinationangle θ increases toward the leading edge 1 a. The blade center Ccorresponds to a bisector of an angle formed between the lines O-D1 andO-D4. Note that FIGS. 5A-5D illustrate the inclination angle θ as anangle formed between a line segment connecting the inner circumferentialedge 1 c and the vertex portion m2 on the outer circumferential side,and the XY-plane. The leading edge region of the rotor blade 1 has ashape adaptable to the blade tip vortex 5 and to a lateral sink flow 9toward the blade outer circumferential portion.

As illustrated in the O-D3 cross section and in the O-D4 cross section,a trailing edge region of the rotor blade 1, which is a region nearer tothe trailing edge 1 b than the blade center C, is inclined towarddownstream of the airflow A, and the inclination angle θ(O-D4) in theO-D4 cross section is greater than the inclination angle θ(O-D3) in theO-D3 cross section. In other words, in the trailing edge region, theinclination angle θ increases toward the trailing edge 1 b. As describedabove, the trailing edge region of the rotor blade 1 has a shape suchthat the blade tip vortex 5 is controlled, and also a centrifugalcomponent 14 of a flow on the inner circumferential portion side, whichhas been subject to a raised pressure, is prevented from leaking,thereby preventing reduction in efficiency.

In addition, in the rotor blade 1 according to the embodiment, acurvature radius value R2 in an outer concave portion that is a regionfrom the vertex portion m2 in the outer circumferential portion to theouter circumferential edge 1 d has a distribution that graduallydecreases from the leading edge 1 a toward the trailing edge 1 b. Inother words, a relationship of R2(O-D1)>R2(O-D2)>R2(O-D3)>R2(O-D4)holds. In addition, the curvature radius value R2 gradually decreases ata rate that decreases toward the trailing edge 1 b.

As described above, the rotor blade 1 according to the embodimentillustrated in FIGS. 4 and 5 has a shape that allows the blade tipvortex 5 generated in an outer circumferential portion to smoothly leavefrom the blade surface, and allows the blade tip vortex 5 to bedispersed without concentration. In this way, the rotor blade 1 reducesturbulence caused by the blade tip vortex 5, thereby making it possibleto curb generation of noise.

The propeller fan 10 is disposed in an inner part of the bell mouth 30,which surrounds the propeller fan to pressurize and regulate theairflow. FIG. 7 is a schematic cross-sectional view of an axial flowblower that uses the rotor blade 1 and a half bell mouth 30 a. The halfbell mouth 30 a surrounds the rotor blades 1 with allowing a regionincluding the leading edge 1 a to be open. FIG. 8 is a schematiccross-sectional view of an axial flow blower that uses the rotor blade 1and a full bell mouth 30 b. The full bell mouth 30 b surrounds the rotorblades 1 circumferentially to entirely cover a side face of the rotorblade 1. The half bell mouth 30 a and the full bell mouth 30 b both havean inlet curved surface Rin, a straight part ST having a cylindricalshape, and an outlet curved surface Rout.

FIG. 9 is a diagram illustrating a distribution of an airflow of theaxial flow blower that uses the rotor blade 1 and the half bell mouth 30a. The axial flow blower including the half bell mouth 30 a isconfigured such that the region including the leading edge 1 a of therotor blade 1 is widely open. This allows the lateral sink flow 9 and apassing-through-blade flow 11 directed from the leading edge 1 a towardthe trailing edge 1 b to flow onto the rotor blade 1. For this reason,the blade tip vortex 5 grows large from the leading edge 1 a side of therotor blade 1. In addition, a condition of the passing-through-bladeflow 11 is changed from the leading edge 1 a to the trailing edge 1 b,so that the blade tip vortex 5 is subjected to significantly differentconditions depending on the axial positions.

FIG. 10 is a diagram illustrating a distribution of an airflow of theaxial flow blower that uses the rotor blade 1 and the full bell mouth 30b. The axial flow blower having the full bell mouth 30 b is configuredsuch that the region including the leading edge 1 a is open to a verylimited extent, thereby almost eliminating the lateral sink flow 9.Thus, almost only the passing-through-blade flow 11 flows toward therotor blade 1. Accordingly, the blade tip vortex 5 does not start to begenerated from the leading edge 1 a, but starts to be generated from apoint where the pressurization has been initiated to some extent.

As described above, even if the same rotor blades 1 are used, a locationof the blade tip vortex 5 is changed depending on the shape of a bellmouth used therefor.

The two types of bell mouths, i.e., the half bell mouth 30 a and thefull bell mouth 30 b may be used in one and the same product. In thiscase, if a rotor blade is designed specifically for each of the types,the cost for the rotor blades is doubled. In the circumstances, the sametype of rotor blades are used even with different bell mouth types, andtherefore, what is required is a rotor blade that can achieve a lownoise level and high efficiency blowing even with different bell mouthtypes.

In response, the present embodiment defines a stagger angle, an angle ofadvance, and a forward tilt angle among the geometry parameters forforming the rotor blade 1 for each of a first region that is an innercircumferential region and a second region that is an outercircumferential region, which are obtained by division of a region fromthe inner circumferential edge 1 c to the outer circumferential edge 1 dof the rotor blade 1, to propose a shape of the first region and a shapeof the second region that can achieve a reduced noise level andimprovement in fan efficiency.

First of all, a stagger angle ξ of the present embodiment will bedescribed. FIG. 11 is a developed sectional view of the rotor blade 1taken along an arc 6-6′ having an arbitrary radius illustrated in FIG.6, in which the cylindrical surface along the arc 6-6′ is developed on aplane. The stagger angle ξ is an angle formed between a chord line 41and a line segment 42. The chord line 41 is a line connecting theleading edge 1 a on a cross-sectional surface 40 of the rotor blade 1and the trailing edge 1 b on the said cross-sectional surface 40. Theline segment 42 is a line that is parallel with the said rotational axisO and intersects the leading edge 1 a.

FIG. 12 is a diagram illustrating an example of a distribution of thestagger angle ξ of the present embodiment. In FIG. 12, the horizontalaxis corresponds to a radius R of the rotor blade 1, and the verticalaxis represents the stagger angle ξ. In FIG. 12, the solid line Lsrepresents the distribution of the stagger angle ξ in the presentembodiment, while the broken line Lv1 represents the distribution of thestagger angle ξ in Comparative Example 1. The left end of the linesegment Ls represents a stagger angle ξc at a radial position Rc of theinner circumferential edge 1 c connected to the boss portion 2, and theright end of the line segment Ls represents a stagger angle ξd at aradial position Rd of the outer circumferential edge 1 d. The staggerangle ξ of the present embodiment has a first stagger angle distributionLs1 in a first region AR1 from the radial position Rc to a boundaryposition Re1, and has a second stagger angle distribution Ls2 differentfrom the first stagger angle distribution Ls1 in a second region AR2from the boundary position Re1 to the radial position Rd.

The first stagger angle distribution Ls1 has a local minimum value ξminat a position Rmin near the boundary position Re1. The position Rmin isbetween the midpoint of the first region AR1 and the boundary positionRe1. The first stagger angle distribution Ls1 has a distribution suchthat the stagger angle ξ gradually decreases from the radial position Rctoward the radial position Rmin and the stagger angle ξ graduallyincreases from the radial position Rmin toward the boundary positionRe1. The second stagger angle distribution Ls2 has a distribution suchthat the stagger angle ξ gradually increases so that the distributionLs2 smoothly connects with the first stagger angle distribution Ls1. Thesecond stagger angle distribution Ls2 has a distribution defined by alinear to quadratic function using the radius R as a parameter. Notethat the second stagger angle distribution Ls2 does not cover a linearfunction. The second stagger angle distribution Ls2 is defined as afunction that is convex downward. The second stagger angle distributionLs2 illustrated in FIG. 12 follows a 1.2-dimensional function. Settingis made such that the second stagger angle distribution Ls2 has a higherabsolute value of an increase rate than that of the decrease rate of thefirst stagger angle distribution Ls1.

FIG. 13 is a diagram illustrating the distribution Lv1 of the staggerangle ξ in Comparative Example 1 and the distribution Lv2 of the staggerangle ξ in Comparative Example 2. Comparative Example 1 and ComparativeExample 2 are described in Patent Literature 2. The distribution Lv1 issuch that the stagger angle ξ increases linearly (in a manner of alinear function) at a constant increase rate. The distribution Lv2 has,similarly to the stagger angle ξ of the present embodiment, adistribution in a first region AR1′ from the radial position Rc of theinner circumferential edge 1 c to a boundary position Re′, and adistribution in a second region AR2′ from the boundary position Re′ tothe radial position Rd of the outer circumferential edge 1 d. In thefirst region AR1′, the stagger angle ξ gradually decreases in the formof a curved line from the radial position Rc to the radial position Re′,and has a local minimum value at the radial position Re′. The staggerangle ξ at the radial position Rc has the maximum value of the staggerangle ξ over the entire range of the rotor blade 1. In the second regionAR2′, the stagger angle ξ gradually increases from the boundary positionRe′ and reaches a local maximum value, and gradually decreases from theradial position of the local maximum value toward the radial positionRd.

FIG. 14 is a developed sectional view illustrating comparison betweenthe stagger angle in Comparative Example 1 and the stagger angle inComparative Example 2 in the first region AR1′. FIG. 14 is a view of therotor blades of Comparative Example 1 and Comparative Example 2 taken atthe radius R1′ illustrated in FIG. 13, in which a cylindrical surface onthe cross section is developed on a plane. The broken line 43corresponds to Comparative Example 1, and the bold solid line 44corresponds to Comparative Example 2. The reference character ξ_(R11)represents the stagger angle at the radius R1′ in Comparative Example 1,and the reference character ξ_(R12) represents the stagger angle at theradius R1′ in Comparative Example 2. FIG. 14 shows that in the firstregion AR1′, the blade is less inclined in Comparative Example 2 than inComparative Example 1.

FIG. 15 is a developed sectional view illustrating comparison betweenthe stagger angle in Comparative Example 1 and the stagger angle inComparative Example 2 in the second region AR2′. FIG. 15 is a view ofthe rotor blades of Comparative Example 1 and Comparative Example 2taken at the radius R2′ illustrated in FIG. 13, in which the cylindricalsurface on the cross section is developed on a plane. The broken line 45corresponds to Comparative Example 1, and the bold solid line 46corresponds to Comparative Example 2. The reference character ξ_(R21)represents the stagger angle at the radius R2′ in Comparative Example 1,and the reference character ξ_(R22) represents the stagger angle at theradius R2′ in Comparative Example 2. FIG. 15 shows that in the secondregion AR2′, the blade is more inclined in Comparative Example 2 than inComparative Example 1.

FIG. 16 is a schematic view illustrating the rotor blade of ComparativeExample 1. FIG. 17 is a schematic view illustrating the rotor blade ofComparative Example 2. As illustrated in FIGS. 16 and 17, a blade heightH2 of Comparative Example 2 is greater than a blade height H1 ofComparative Example 1 at the outer circumferential edge.

As described above, by use of the stagger angle distribution as inComparative Example 2, the blade angle is set to an appropriate valuefor a flow in each of a high flow rate region and a low flow rateregion, thereby resulting in a reduced noise level and higherefficiency. However, as illustrated in FIG. 17, the blade height islarger in an outer circumferential portion. This will present no problemwith a product having enough margin space in the height direction, butwhen a further reduced height is required, it will be difficult to use astagger angle distribution as shown in Comparative Example 2.

In the circumstances, the present embodiment uses the stagger angledistribution as illustrated in FIG. 12 to thereby make it possible tolimit the height of the outer circumferential portion that can causeincrease in height of a product and to also make the stagger angledistribution more appropriate. The blade in the present embodiment has ashape that is similar to the shape in Comparative Example 1 on the outercircumferential portion side and similar to the shape in ComparativeExample 2 on the inner circumferential portion side. Therefore, thepresent embodiment can limit the height of the outer circumferentialportion, and match the angle of the blade with the angle of the flow.This can reduce leading edge separation and trailing vortex loss of theblade, and can thus achieve a reduced noise level and higher efficiency.Moreover, the use of a distribution having a local minimum value in thefirst region AR1 where a flow rate is lower enables the stagger angle inthe second region AR2 to be adjusted, and also enables the first regionAR1 to smoothly connect with the second region AR2.

Next, an angle of advance δ_(θ) in the present embodiment will bedescribed. FIG. 18 is a plan view for describing the angle of advanceδ_(θ). In FIG. 18, the reference character g designates the chord centerline. The chord center line g is a line that connects the midpointsbetween the leading edge 1 a and the trailing edge 1 b at every radialposition from the inner circumferential edge 1 c to the outercircumferential edge 1 d. An angle formed between a straight line 51connecting the rotational axis O and the said midpoint 52 on the innercircumferential edge 1 c, and a straight line 54 connecting anintersection point 53 between an arc on an arbitrary radius and thechord center line g and the rotational axis O is defined as an angle ofadvance δ_(θ).

FIG. 19 is a graph illustrating an example of a distribution of theangle of advance δ_(θ) in the present embodiment, and a distribution ofthe angle of advance δ_(θ) of Comparative Example 3. The solid linecorresponds to the present embodiment, and the broken line correspondsto Comparative Example 3. In the case of Comparative Example 3, theangle of advance δ_(θ) linearly increases from the inner circumferentialedge 1 c to the outer circumferential edge 1 d. As illustrated in FIG.18, use of the distribution of Comparative Example 3 causes the outercircumferential portion to have a delta wing shape. A delta wing shapecauses a separation vortex to be generated from the delta wing portion,and the generated separation vortex can reduce or prevent generation ofa leading edge separation vortex and a blade tip vortex, thereby makingit possible to achieve a reduced noise level.

FIG. 20 is a diagram illustrating the blade shape in Comparative Example3 when an increase rate of the angle of advance is low. FIG. 21 is adiagram illustrating the blade shape in Comparative Example 3 when anincrease rate of the angle of advance is greater than the increase rateof FIG. 20. The length of the inner circumferential edge 1 c in FIG. 20is the same as the length of the inner circumferential edge 1 c in FIG.21. In addition, the length of the outer circumferential edge 1 d inFIG. 20 is the same as the length of the outer circumferential edge 1 din FIG. 21. The angle of advance δ_(θ) 2 on the outer circumferentialedge 1 d in FIG. 21 is greater than the angle of advance δ_(θ) 1 on theouter circumferential edge 1 d in FIG. 20.

As illustrated in FIG. 21, use of a linear distribution in which anincrease rate of the angle of advance δ_(θ) is higher can achieve afurther reduced noise level than the case of FIG. 20, but leads to aproblem such as insufficient strength of a root part of the blade, sothat a large angle of advance cannot be set for the outercircumferential portion.

As illustrated by the solid line of FIG. 19, the angle of advance of therotor blade according to the present embodiment has differentdistributions in the first region AR1 and in the second region AR2. Thefirst region AR1 is an area from the radius Rc corresponding to theinner circumferential edge 1 c to a boundary position Re2. The secondregion AR2 is an area from the boundary position Re2 to the outercircumferential edge 1 d. The angle of advance δ_(θ) has, in the firstregion AR1, a linear distribution that gradually increases from theradial position Rc toward the boundary position Re2. The angle ofadvance δ_(θ) has, in the second region AR2, a linear to quadraticfunction distribution that gradually increases from the boundaryposition Re2 toward the radial position Rd. In other words, the angle ofadvance δ_(θ) in the second region AR2 follows a linear to quadraticfunction using the radius R as a parameter. Note that the angle ofadvance δ_(θ) in the second region AR2 does not cover a linear function.The angle of advance δ_(θ) in the second region AR2 is defined as alinear to quadratic function that is convex downward. FIG. 19 shows a1.2-dimensional function as a distribution function in the second regionAR2. The linear distribution in the first region AR1 smoothly connectswith a distribution of the 1.2-dimensional function in the second regionAR2. The distribution of the angle of advance δ_(θ) in the second regionAR2 desirably has an increase rate higher than the increase rate of thedistribution of the angle of advance δ_(θ) in the first region AR1.

FIG. 22 illustrates an example of the shape of the rotor blade in thecase of use of the angle-of-advance distribution according to thepresent embodiment illustrated in FIG. 19. Use of the angle-of-advancedistribution according to the present embodiment enables a delta wingshape to be ensured for reducing the noise level in the blade outercircumferential portion, and an area of the blade to be increased in theblade inner circumferential portion thereby to increase the strength ofthe blade root portion.

Next, a forward tilt angle δz of the present embodiment will bedescribed. FIG. 23 is a diagram for describing a definition of a forwardtilt angle δz. FIG. 23 is a revolved projection of a rotor blade havinga constant forward tilt angle δz projected onto the plane including therotational axis O and the X-axis. The forward tilt angle δz is an angleformed between a chord center line g′ and a plane perpendicular to therotational axis O of the rotor blade 1. A direction toward the upstreamside of the flow is defined as positive for the angle δz. FIG. 24 is adiagram illustrating the chord center line g of the rotor blade 1according to the present embodiment in which the blade outercircumferential portion is bent toward the upstream direction side ofthe flow, and shows a revolved projection of the rotor blade projectedonto the plane including the rotational axis O and the X-axis.

FIG. 25 is a graph illustrating an example of a distribution of theforward tilt angle δz of the present embodiment, and a distribution ofthe forward tilt angle δz of Comparative Example 4. The solid linecorresponds to the present embodiment, and the broken line correspondsto Comparative Example 4. Comparative Example 4 is described in PatentLiterature 1. In Comparative Example 4 and in the present embodiment,the forward tilt angle δz has a distribution in the first region AR1from the radial position Rc of the inner circumferential edge 1 c to aboundary position Re3, and a distribution in the second region AR2 fromthe boundary position Re3 to the radial position Rd of the outercircumferential edge 1 d.

In Comparative Example 4, the forward tilt angle δz has a constant valueδz1 in the first region AR1, and the forward tilt angle δz has adistribution with further inclination toward an upstream side of theflow in the second region AR2 so as to follow an n-dimensional function(1≤n) using the radius R as a parameter. By use of a forward tilt angledistribution as shown in Comparative Example 4, the blade tip vortexgenerated on the blade outer circumferential portion can be controlledand turbulence caused by the blade tip vortex can be reduced, and thusmaking it possible to reduce a noise level.

In this regard, in the present embodiment, the forward tilt angle δz hasa constant value δz1 in the first region AR1 similarly to ComparativeExample 4, while the forward tilt angle δz in the second region AR2follows a distribution based on a quadratic to quintic function usingthe radius R as a parameter, thereby achieving a further reduced noiselevel. In FIG. 25, in the second region AR2, of Comparative Example 4 isshown as following a quadratic function, and the present embodiment isshown as following a cubic function. Of quadratic to quintic functions,quadratic to cubic functions are particularly suitable.

Referring to FIGS. 26 to 37, results of evaluation of the rotor blade ofthe present embodiment will be described. FIGS. 26 to 37 illustrateevaluation results when rotor blades having a diameter of 260 (mm) arerotated at a constant rotational speed. The specific noise level Kt witha total pressure as a reference, the specific noise level Ks with astatic pressure as a reference, the fan efficiency Et with a totalpressure as a reference, and the fan efficiency Es with a staticpressure as a reference, which are used in FIGS. 26 to 37 are calculatedvalues defined by the following expressions.

Kt=SPLA−10 Log(Q·PT ^(2.5))

Q: airflow rate [m³/min]

PT: total pressure [Pa]

SPLA: noise characteristic (after Correction A) [dB]

Ks=SPLA−10 Log(Q·PS ^(2.5))

Q: airflow rate [m³/min]

PS: static pressure [Pa]

SPLA: noise characteristic (after Correction A) [dB]

Et=(PT·Q)/(60·PW)

Q: airflow rate [m³/min]

PT: total pressure [Pa]

PW: shaft power [W]

Es=(PS·Q)/(60·PW)

Q: airflow rate [m³/min]

PS: static pressure [Pa]

PW: shaft power [W]

Note that Correction A refers to correction to reduce the sound level atlow frequencies to fit the characteristics of human auditory sense, andcorresponds to, for example, correction based on Characteristic Adetermined in JIS C 1502-1990.

FIGS. 26A to 26C are diagrams illustrating different kinds ofcharacteristics of the rotor blade of Comparative Example 5, the rotorblade of Example 1 in the embodiment, and the rotor blade of Example 2in the embodiment in the case of use of the half bell mouth 30 aillustrated in FIG. 7. Comparative Example 5 is represented by thebroken line. The embodiment's Example 1 is represented by the solidline. The embodiment's Example 2 is represented by the dashed-and-dottedline. FIG. 26A illustrates relationships between the fan efficiency Esand the airflow rate. FIG. 26B illustrates relationships between thespecific noise level Kt and the airflow rate. FIG. 26C illustratesrelationships between the static pressure PS and the airflow rate. Therotor blade of Comparative Example 5 has the rotor blade shapeillustrated in FIGS. 4 and 5, has the stagger angle distribution Lv1represented by the broken line in FIG. 12, has the angle-of-advancedistribution represented by the broken line in FIG. 19, and has theforward tilt angle distribution represented by the broken line in FIG.25. The rotor blade of the embodiment's Example 1 and the rotor blade ofthe embodiment's Example 2 each correspond to the rotor bladeillustrated in FIGS. 4 and 5, have the stagger angle distributionrepresented by the solid line in FIG. 12, have the angle-of-advancedistribution represented by the solid line in FIG. 19, and have theforward tilt angle distribution represented by the solid line in FIG.25. The rotor blade of Example 1 has, in the second region AR2, astagger angle distribution that follows a 1.2-dimensional function beingset, has, in the second region AR2, a angle-of-advance distribution thatfollows a 1.2-dimensional function being set, and has, in the secondregion AR2, a forward tilt angle distribution that follows a3-dimensional function being set. The rotor blade of Example 2 has, inthe second region AR2, a stagger angle distribution that follows a2-dimensional function being set, has, in the second region AR2, aangle-of-advance distribution that follows a 2-dimensional functionbeing set, and has, in the second region AR2, a forward tilt angledistribution that follows a 3-dimensional function being set.

In the case of use of the half bell mouth 30 a, the rotor blades ofExamples 1 and 2 in the embodiment enable, as illustrated in FIG. 26C,an open airflow rate at the open point corresponding to [staticpressure=0] to be improved by +2(%), and the static pressure to beimproved by up to +7.8(%) as compared to Comparative Example 5. Inaddition, as illustrated in FIG. 26A, the fan efficiency Es can beimproved by up to +3.5 points. Moreover, as illustrated in FIG. 26B, thespecific noise level Kt can be improved by up to −1 (dB).

FIGS. 27A to 27C are diagrams illustrating different kinds ofcharacteristics of the rotor blade of Comparative Example 5 describedabove, the rotor blade of Example 1 in the embodiment described above,and the rotor blade of Example 2 in the embodiment described above inthe case of use of the full bell mouth 30 b illustrated in FIG. 8.Comparative Example 5 is shown by the broken line. The embodiment'sExample 1 is shown by the solid line. The embodiment's Example 2 isshown by the dashed-and-dotted line. FIG. 27A illustrates relationshipsbetween the fan efficiency Es and the airflow rate. FIG. 27B illustratesrelationships between the specific noise level Kt and the airflow rate.FIG. 27C illustrates relationships between the static pressure PS andthe airflow rate.

In the case of use of the full bell mouth 30 b, the rotor blades ofExamples 1 and 2 in the embodiment enable, as illustrated in FIG. 27C,an open airflow rate to be improved by +3.6(%) and a static pressure tobe improved by up to +7.8(%) as compared to Comparative Example 5. Inaddition, as illustrated in FIG. 27A, the fan efficiency Es can beimproved by up to +7 points. Moreover, as illustrated in FIG. 27B, thespecific noise level Kt can be improved by up to −1.5 (dB).

The evaluation results of FIGS. 26 and 27 indicate that the rotor bladesof Examples 1 and 2 enable the blowing characteristic, the noisecharacteristic, and the fan efficiency characteristic to be improvedirrespective of the form of a bell mouth used therein.

FIGS. 28A to 28C are diagrams illustrating different kinds ofcharacteristics of the rotor blade of Comparative Example 5 describedabove, the rotor blade of Example 1 in the embodiment described above,and the rotor blade of Example 3 in the embodiment in the case of use ofthe half bell mouth 30 a illustrated in FIG. 7. Comparative Example 5 isshown by the broken line. The embodiment's Example 1 is shown by thesolid line. The embodiment's Example 3 is represented by thedashed-and-dotted line. FIG. 28A illustrates relationships between thefan efficiency Es and the airflow rate. FIG. 28B illustratesrelationships between the specific noise level Kt and the airflow rate.FIG. 28C illustrates relationships between the static pressure PS andthe airflow rate. Similarly to the rotor blades of Examples 1 and 2 inthe embodiment, the rotor blade of Example 3 in the embodiment has arotor blade shape illustrated in FIGS. 4 and 5, has the stagger angledistribution represented by the solid line in FIG. 12, has theangle-of-advance distribution represented by the solid line in FIG. 19,and has the forward tilt angle distribution represented by the solidline in FIG. 25. The rotor blade of the embodiment's Example 3 has, inthe second region AR2, a stagger angle distribution that follows afunction to be set having a degree of 1.2, has, in the second regionAR2, a angle-of-advance distribution that follows a function to be sethaving a degree of 1.2, and has, in the second region AR2, a forwardtilt angle distribution that follows a function to be set having adegree of 4.

In the case of use of the half bell mouth 30 a, the rotor blade ofExample 3 enables, as illustrated in FIG. 28C, the open airflow rate tobe improved by +2.2(%) and the static pressure to be improved by up to+5.9(%) as compared to Comparative Example 5. In addition, asillustrated in FIG. 28A, the fan efficiency Es can be improved by up to+4 points. Moreover, as illustrated in FIG. 28B, the specific noiselevel Kt can be improved by up to −3 (dB).

FIGS. 29A to 29C are diagrams illustrating different kinds ofcharacteristics of the rotor blade of Comparative Example 5 describedabove, the rotor blade of Example 1 in the embodiment described above,and the rotor blade of Example 3 in the embodiment described above inthe case of use of the full bell mouth 30 b illustrated in FIG. 8.Comparative Example 5 is shown by the broken line. The embodiment'sExample 1 is shown by the solid line. The embodiment's Example 3 isshown by the dashed-and-dotted line. FIG. 29A illustrates relationshipsbetween the fan efficiency Es and the airflow rate. FIG. 29B illustratesrelationships between the specific noise level Kt and the airflow rate.FIG. 29C illustrates relationships between the static pressure PS andthe airflow rate.

In the case of use of the full bell mouth 30 b, the rotor blade ofExample 3 in the embodiment enables, as illustrated in FIG. 29C, theopen airflow rate to be improved by +3(%) and the static pressure to beimproved by up to +6.9(%) as compared to Comparative Example 5. Inaddition, as illustrated in FIG. 29A, the fan efficiency Es can beimproved by up to +12 points. Moreover, as illustrated in FIG. 29B, thespecific noise level Kt can be improved by up to −2 (dB).

The evaluation results of FIGS. 28 and 29 indicate that the rotor bladeof Example 3 enables the blowing characteristic, the noisecharacteristic, and the fan efficiency characteristic to be improvedirrespective of the form of a bell mouth used therefor.

Next, referring to FIGS. 30 to 37, the degree of the forward tilt of therotor blade of Example 1 in the embodiment will be described. FIG. 30 isa graph illustrating the specific noise characteristics at the openpoint of the rotor blade of Comparative Example 5 described above andthe rotor blade of the embodiment's Example 1 described above in thecase of use of the half bell mouth 30 a illustrated in FIG. 7. FIG. 30illustrates the relationships between the degree of the function usedfor the forward tilt angle distribution in the second region AR2 and thespecific noise level Kt at the open point. The degree has been changedfrom 1.2 to 5. Note that the forward tilt angle distribution in thesecond region AR2 for the rotor blade of Comparative Example 5 follows aquadratic function as described above. As illustrated in FIG. 30, therotor blade of the embodiment's Example 1 exhibits a specific noiselevel Kt higher than that of Comparative Example 5 when the degree is1.2, but a specific noise level Kt improved as compared to ComparativeExample 5 in the range of degree from 2 to 7.

FIG. 31 is a graph illustrating the fan efficiency characteristics atthe open point of the rotor blade of Comparative Example 5 describedabove and the rotor blade of the embodiment's Example 1 described abovein the case of use of the half bell mouth 30 a illustrated in FIG. 7.FIG. 31 illustrates the relationships between the degree of the functionused for the forward tilt angle distribution in the second region AR2and the fan efficiency Et at the open point. The degree has been changedfrom 1.2 to 5. As illustrated in FIG. 31, the rotor blade of theembodiment's Example 1 exhibits a fan efficiency Et improved as comparedto Comparative Example 5 in terms of all the degrees.

FIG. 32 is a graph illustrating the minimum specific noisecharacteristics at the time of application of static pressure of therotor blade of Comparative Example 5 described above and the rotor bladeof the embodiment Example 1 described above in the case of use of thehalf bell mouth 30 a illustrated in FIG. 7. FIG. 32 illustrates therelationships between the degree of the function used for the forwardtilt angle distribution in the second region AR2 and the minimumspecific noise level Ks at the time of application of static pressure.The degree has been changed from 1.2 to 5. As illustrated in FIG. 32,the specific noise level Ks is higher than that of Comparative Example 5when the degree is 1.2, but the specific noise level Ks is improved ascompared to Comparative Example 5 in the range of degree from 2 to 5.

FIG. 33 is a graph illustrating the maximum fan efficiencycharacteristics of the rotor blade of Comparative Example 5 describedabove and the rotor blade of the embodiment's Example 1 described abovein the case of use of the half bell mouth 30 a illustrated in FIG. 7.FIG. 33 illustrates the relationships between the degree of the functionused for the forward tilt angle distribution in the second region AR2and the maximum fan efficiency Esmax. The degree has been changed from1.2 to 5. As illustrated in FIG. 33, the maximum fan efficiency Esmax isimproved as compared to Comparative Example 5 in terms of all thedegrees.

FIG. 34 is a graph illustrating the specific noise characteristics atthe open point of the rotor blade of Comparative Example 5 describedabove and the rotor blade of the embodiment's Example 1 described abovein the case of use of the full bell mouth 30 b illustrated in FIG. 8.FIG. 34 illustrates the relationships between the degree of the functionused for the forward tilt angle distribution in the second region AR2and the specific noise level Kt at the open point. The degree has beenchanged from 1.2 to 5. As illustrated in FIG. 34, the rotor blade ofExample 1 in the embodiment exhibits a specific noise level Kt improvedas compared to Comparative Example 5 in terms of all the degrees.

FIG. 35 is a graph illustrating the fan efficiency characteristics ofthe rotor blade of Comparative Example 5 described above and the rotorblade of the embodiment's Example 1 described above at the open point inthe case of use of the full bell mouth 30 b illustrated in FIG. 8. FIG.35 illustrates the relationships between the degree of the function usedfor the forward tilt angle distribution in the second region AR2 and thefan efficiency Et at the open point. The degree has been changed from1.2 to 5. As illustrated in FIG. 35, the rotor blade of Example 1 in theembodiment exhibits a fan efficiency Et almost the same as that ofComparative Example 5 when the degree is 1.2. In addition, the rotorblade of the embodiment's Example 1 exhibits a fan efficiency Etdegraded with respect to that of Comparative Example 5 when the degreeis 5, but a fan efficiency Et improved as compared to ComparativeExample 5 over the range of degree from 2 to 4.

FIG. 36 is a graph illustrating the minimum specific noisecharacteristics at the time of application of static pressure of therotor blade of Comparative Example 5 described above and the rotor bladeof Example 1 in the embodiment described above in the case of use of thefull bell mouth 30 b illustrated in FIG. 8. FIG. 36 illustrates therelationships between the degree of the function used for the forwardtilt angle distribution in the second region AR2 and the minimumspecific noise level Ks at the time of application of static pressure.The degree has been changed from 1.2 to 5. As illustrated in FIG. 36,the rotor blade of the embodiment's Example 1 exhibits a specific noiselevel Ks improved as compared to Comparative Example 5 in terms of allthe degrees.

FIG. 37 is a graph illustrating the maximum fan efficiencycharacteristics of the rotor blade of Comparative Example 5 describedabove and the rotor blade of Example 1 in the embodiment described abovein the case of use of the full bell mouth 30 b illustrated in FIG. 8.FIG. 37 illustrates the relationships between the degree of the functionused for the forward tilt angle distribution in the second region AR2and the maximum fan efficiency Esmax. The degree has been changed from1.2 to 5. As illustrated in FIG. 37, the maximum fan efficiency Esmax isimproved as compared to Comparative Example 5 over the range of degreefrom 2 to 5.

As illustrated in FIGS. 30 to 37, the present embodiment enables theblowing characteristic, the noise characteristic, and the fan efficiencycharacteristic to be improved irrespective of the form of a used bellmouth as long as a distribution of the forward tilt angle δz in thesecond region follows a quadratic to quintic function.

As described above, according to the present embodiment, the staggerangle ξ of the rotor blade has a first stagger angle distribution havinga local minimum value in an area from the inner circumferential edge tothe first boundary position Re1, and has a second stagger angledistribution that increases toward the said outer circumferential edgeand follows an n-dimensional function using the radius of the said rotorblade as a parameter in an area from the first boundary position Rel tothe outer circumferential edge. “n”, which is used in the n-dimensional,is a value ranging from 1 to 2, but exclusive of 1. Thus, the presentembodiment can limit the height of the outer circumferential portion,and can also achieve a reduced noise level and higher efficiency.

In addition, in the present embodiment, the angle of advance δ_(θ) ofthe rotor blade has a first angle-of-advance distribution that linearlyincreases in an area from the inner circumferential edge to the secondboundary position Re2, and has a second angle-of-advance distributionthat increases toward the said outer circumferential edge and follows anm-dimensional function using the radius as a parameter in an area fromthe second boundary position Re2 to the outer circumferential edge,where m is a value ranging from 1 to 2, but exclusive of 1. Therefore,the present embodiment enables a delta wing shape to be ensured forreducing the noise level in the blade outer circumferential portion, andat the same time, the strength at the blade root portion to beincreased.

Moreover, in the present embodiment, the forward tilt angle δz of therotor blade has a first forward tilt angle distribution having aconstant value in an area from the inner circumferential edge to thethird boundary position Re3, and has a second forward tilt angledistribution that increases toward the outer circumferential edge andfollows a p-dimensional function using the radius as a parameter in anarea from the third boundary position Re3 to the outer circumferentialedge, where p is a value ranging from 2 to 5. Therefore, the presentembodiment can achieve a further reduced noise level.

The configurations described in the foregoing embodiment are merelyexamples of various aspects of the present invention, and can becombined with other publicly known techniques and partially omittedand/or modified without departing from the spirit of the presentinvention.

REFERENCE SIGNS LIST

1 rotor blade; 1 a leading edge; 1 b trailing edge; 1 c innercircumferential edge; 1 d outer circumferential edge; 2 boss portion; 5blade tip vortex; 10 propeller fan; 30 bell mouth; 30 a half bell mouth;30 b full bell mouth; 100 axial flow blower; g chord center line; Orotational axis; W rotation direction; ξ stagger angle; δ_(θ) angle ofadvance; δz forward tilt angle.

1. A propeller fan including a boss portion that is driven rotationally,and more than one rotor blade radially attached to the boss portion togenerate an airflow in a rotational axis direction, wherein a radialcross section of the rotor blade on an inner circumferential portionside of the rotor blade has a shape convex against a direction of theairflow, and a radial cross section of the rotor blade on an outercircumferential portion side of the rotor blade has a shape concavealong the direction of the airflow, the radial cross section of therotor blade is inclined toward an upstream side of the airflow in aleading edge side region with an inclination angle increasing toward aleading edge, and is inclined toward a downstream side of the airflow ina trailing edge side region with the inclination angle increasing towarda trailing edge, and a stagger angle of the rotor blade has a firststagger angle distribution having a local minimum value in a region froman inner circumferential edge to a first boundary position, and has asecond stagger angle distribution that increases toward an outercircumferential edge and follows an n-dimensional function using aradius of the rotor blade as a parameter in a region from the firstboundary position to the outer circumferential edge, where n is a valueranging from 1 to 2 and exclusive of
 1. 2. The propeller fan accordingto claim 1, wherein an angle of advance of the rotor blade has a firstangle-of-advance distribution that linearly increases in a region fromthe inner circumferential edge to a second boundary position, and has asecond angle-of-advance distribution that increases toward the outercircumferential edge and follows an m-dimensional function using theradius as a parameter in a region from the second boundary position tothe outer circumferential edge, where m is a value ranging from 1 to 2and exclusive of
 1. 3. The propeller fan according to claim 1, wherein aforward tilt angle of the rotor blade has a first forward tilt angledistribution having a constant value in a region from the innercircumferential edge to a third boundary position, and has a secondforward tilt angle distribution that increases toward the outercircumferential edge and follows a p-dimensional function using theradius as a parameter in a region from the third boundary position tothe outer circumferential edge, where p is a value ranging from 2 to 5.4. The propeller fan according to claim 1, wherein the second staggerangle distribution changes at a rate higher than a rate of change in thefirst stagger angle distribution.
 5. The propeller fan according toclaim 2, wherein the second angle-of-advance distribution increases at arate higher than a rate of increase in the first angle-of-advancedistribution.
 6. An axial flow blower comprising: the propeller fanaccording to claim 1; a motor to rotationally drive the boss portion ofthe propeller fan; and a body including a bell mouth disposed around thepropeller fan.
 7. The propeller fan according to claim 2, wherein aforward tilt angle of the rotor blade has a first forward tilt angledistribution having a constant value in a region from the innercircumferential edge to a third boundary position, and has a secondforward tilt angle distribution that increases toward the outercircumferential edge and follows a p-dimensional function using theradius as a parameter in a region from the third boundary position tothe outer circumferential edge, where p is a value ranging from 2 to 5.8. The axial flow blower according to claim 6, wherein an angle ofadvance of the rotor blade has a first angle-of-advance distributionthat linearly increases in a region from the inner circumferential edgeto a second boundary position, and has a second angle-of-advancedistribution that increases toward the outer circumferential edge andfollows an m-dimensional function using the radius as a parameter in aregion from the second boundary position to the outer circumferentialedge, where m is a value ranging from 1 to 2 and exclusive of
 1. 9. Theaxial flow blower according to claim 6, wherein a forward tilt angle ofthe rotor blade has a first forward tilt angle distribution having aconstant value in a region from the inner circumferential edge to athird boundary position, and has a second forward tilt angledistribution that increases toward the outer circumferential edge andfollows a p-dimensional function using the radius as a parameter in aregion from the third boundary position to the outer circumferentialedge, where p is a value ranging from 2 to
 5. 10. The axial flow bloweraccording to claim 8, wherein a forward tilt angle of the rotor bladehas a first forward tilt angle distribution having a constant value in aregion from the inner circumferential edge to a third boundary position,and has a second forward tilt angle distribution that increases towardthe outer circumferential edge and follows a p-dimensional functionusing the radius as a parameter in a region from the third boundaryposition to the outer circumferential edge, where p is a value rangingfrom 2 to
 5. 11. The axial flow blower according to claim 6, wherein thesecond stagger angle distribution changes at a rate higher than a rateof change in the first stagger angle distribution.
 12. The axial flowblower according to claim 8, wherein the second angle-of-advancedistribution increases at a rate higher than a rate of increase in thefirst angle-of-advance distribution.